wlan2eth/bridge/bridge-lan.sh

#!/bin/bash

SOURCE=${BASH_SOURCE[0]}
while [ -L "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symlink
  DIR=$(cd -P "$(dirname "$SOURCE")" >/dev/null 2>&1 && pwd)
  SOURCE=$(readlink "$SOURCE")
  [[ $SOURCE != /* ]] && SOURCE=$DIR/$SOURCE # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
done
DIR=$(cd -P "$(dirname "$SOURCE")" >/dev/null 2>&1 && pwd)

if [[ -f "$DIR/../config/config.sh" ]]; then
  . "$DIR/../config/config.sh"
else
  echo "$DIR/../config/config.sh missing!"
  exit 1
fi

if [ "$(id -u)" -ne 0 ]; then
  echo 'This script must be run as root.' >&2
  exit 1
fi

. "$DIR/get-dhcp-dns.sh"

# ==============================================================================

PRIVATE_LAN_IP="192.168.2.1"
BRIDGED_CLIENT_IP="192.168.2.2"

# Configure the wired interface with the bridge IP address
ifconfig $ETH_IFACE $PRIVATE_LAN_IP netmask 255.255.255.0 up

# Mirror the DNS servers to the private LAN
DHCP_DNS=($(get_dns_servers "$WLAN_IFACE"))
if [ -n "$DHCP_DNS" ]; then
  dns_servers_config=""
  for server in "${DHCP_DNS[@]}"; do
    dns_servers_config+="server=$server"$'\n'
  done

  dhcp_opt_6_config="dhcp-option=6"
  for server in "${DHCP_DNS[@]}"; do
    dhcp_opt_6_config+=",$server"
  done
  echo "Mirrored WLAN DHCP DNS servers: ${DHCP_DNS[*]}"
else
  dns_servers_config="""server=1.1.1.1
server=1.0.0.1"""
  dhcp_opt_6_config=""
fi

# Also mirror DNS domain
DHCP_DNS_DOMAIN=$(get_dns_domain $WLAN_IFACE)
if [ -n "$DHCP_DNS_DOMAIN" ]; then
  dns_domain_config="domain=$DHCP_DNS_DOMAIN"
  echo "Mirrored WLAN DHCP DNS domain: $DHCP_DNS_DOMAIN"
else
  dns_domain_config=""
fi

cat >/etc/dnsmasq.conf <<EOL
interface=$ETH_IFACE
domain-needed
bogus-priv
no-resolv
$dns_servers_config
$dhcp_opt_6_config
$dns_domain_config
listen-address=::1,127.0.0.1,$PRIVATE_LAN_IP
expand-hosts
dhcp-range=$PRIVATE_LAN_IP,$BRIDGED_CLIENT_IP,12h
dhcp-option=option:router,$PRIVATE_LAN_IP
dhcp-authoritative
dhcp-leasefile=/var/lib/dnsmasq/dnsmasq.leases
EOL
echo "Wrote to /etc/dnsmasq.conf"

# Configure NAT to forward traffic between the private LAN and the WLAN
iptables -X
iptables -F
iptables -t nat -X
iptables -t nat -F
echo "Reset iptables"

# Route/forward traffic between nets
iptables -I INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -I POSTROUTING -o $WLAN_IFACE -j MASQUERADE
echo "Created iptables to route traffic between nets"

# Port forward everything to the single client
iptables -t nat -A PREROUTING -i $WLAN_IFACE -j DNAT --to-destination $BRIDGED_CLIENT_IP
iptables -t nat -A POSTROUTING -o $ETH_IFACE -j MASQUERADE
echo "Port forwarded everything to the single bridged client"

echo -en "\nRestarting dnsmasq..."
service systemd-resolved stop
# systemctl enable --now dnsmasq
systemctl restart dnsmasq
echo -e "\n"
sleep 5
systemctl status --no-pager dnsmasq